The invention relates to a rotational working cylinder comprising a shaft arranged concentrically within the working cylinder and driven out of the working cylinder with at least one end of it, a piston being divided into two piston portions perpendicularly to the shaft and the piston portions being held in tensed position in respect to each other, forced trajectories between the working cylinder and the piston portions as well as between the piston portions and the shaft, respectively, wherein at least one of the forced trajectories is formed as a longitudinal spiral path.
In various fields of the industry, it is often required to provide rotary motion, including non-continuous rotation as well as displacement with a predetermined angular range. In particular cases, the rotary motion should be an alternating one with selectively opposite rotational directions. In these cases, large torques as well as small angular velocities can occur.
The best mode for fulfilling these needs is provided by a rotational ram cylinder as described in e.g. West-German Pat. No. 23 38 745. In the closed inner operating chamber of this ram cylinder are located a piston which is driven to move in alternating longitudinal motion by a hydraulic or pneumatic medium and a shaft being attached to the piston. At least one end of the shaft extends out of the operating chamber, and in this solution, at least one of the mechanical connections between the ram cylinder and the piston or between the piston and the shaft is formed as a spiral path rising in the longitudinal direction of the shaft.
However, in the praxis, it has been found that the backlash or play in these ram cylinders are too big for the applications in modern apparatuses such as in that of the robot technics. The clearence being necessary between the parts moving in respect to each other results in an insufficient accuracy of the convertion of the longitudinal motion of the piston into the rotational motion of the shaft.
The problems resulting from the insufficient accuracy have to be faced in the case of rotary converters having worm gears being previously more often used for movement conversion. Therefore, it has been suggested to divide the nut arranged on the worm spindle into two nut portions perpendicularly to the shaft as described e.g. in West-German Pat. No. 11 51 420 and West-German Pat. No. 27 01 717. In these solutions, the backlash is suggested to be lessened by holding the nut portions in tensioned position in respect to each other. For this, springs and magnet coils are arranged between the nut portions for tensioning them in respect to each other.
However, these solutions fail to work as awaited. The tensioned position can be maintained only in a relatively narrow load range because of the force of the springs and magnet coils which can be exerted between the nut portions. If this force is chosen to be big for carrying big loads by the worm gear, the threaded surfaces of the nut portions and the worm spindel are pressed on each other with a quite big normal force. This results in an enlargened frictional resistance when the surfaces have to be moved on each other and in an increased wear or abrasion of the threaded surfaces. The first deficiency necessitates a relatively high driving force, especially at the beginning of the relative movement between the threaded surfaces, and the second one causes a shorter endurance of the traditional rotary converters. If, in contrast, the force exerted between the nut portions is chosen to be small, the rotary converter can be used only for small loads since the smaller tensioning force can not withstand the forces urging one of the nut portions away from the threaded surface of the worm spindle. If this occures, the worm gear is no more free of backlash.
Further to this, the force exerted between the nut portions is dependent on the actual distance between the nut portions when using springs or magnet coils for making the worm gear free of the backlash. Therefore, the range of loads with which the traditional rotary converter can be operated changes in time since, depending on the wear of the constructional parts, the distance between the nut portions is varying. Followingly, if the rotary converter is faultless in one day, in the next it can have a backlash which can not be permitted, especially in robots. This makes the operational security of the known rotary converters insufficient.
Nevertheless, the rotary converters using worm gears have a lot of disadvantages as described in e.g. West-German Pat. No. 23 38 745 which are avoided with the solution as given in this patent. However, the elimination of the backlash in this kind of ram cylinders is not solved. This defficiency greatly limits the application possibilities of these modern rotational ram cylinders.
The main object of this invention is to eliminate the defficiencies of the above mentioned known solutions and to provide rotational working cylinder which is free of the backlash of the traditional rotational ram cylinders and which can be used for loads in a much wider range. Object of the invention is to provide an arrangement with which the load bearing capacity is not limited by the means provided for the elimination of the backlash but by other constructional features of the rotational working cylinder. Further object is to provide a construction which is easy and simple to manufacture and which has a sufficient operational security.
According to the improvement in this invention, the piston portions of the piston being divided into two portions are locked in relation to each other for maintaining the tensed position of the portions in all operational positions and loads of the working cylinder. The main importance of this solution is in that the backlash resulting from the necessary clearence between the piston and the cylinder as well as between the piston and the shaft remains eliminated during the whole operation cycle of the rotational working cylinder irrespective of the load to be carried by the working cylinder and of the direction and speed of rotation of the shaft of the working cylinder.
In a preferred embodiment, a locking means is provided between the piston portions for their locked relation and the locking means is operated by a hydraulic working agent of the rotational working cylinder.
In this case, it can be preferred when at least one cylinder hole formed as a blind hole and therein a piston are provided in each piston portion, and middle axes of the cylinder holes are on the same diameter around the shaft of the working cylinder, and the cylinder holes of the one piston portion are turned towards and are coaxial with the cylinder holes of the other piston portion, and the cylinder holes are connected through a bore to a working chamber of the rotational working cylinder with which the piston portion containing the cylinder hole is in contact, and the bore is closeable by a non-return valve, and the piston arranged slideably within the cylinder hole in a sealed manner has an inclined end surface in relation to the middle axis of the cylinder hole, and the inclined end surfaces of the pistons of the opposite cylinder holes are lain on each other. The non-return valve can be formed according to the invention as a ball arranged at an inner opening of the bore connecting the cylinder hole to the working chamber and the ball is loaded by a spring, an other end of which being lain on the piston of the cylinder hole.
In another preferred embodiment, at least one throughbore is provided in each piston portion which is closeable by a non-return valve permitting an inward flow of the working agent into a room provided between the piston portions. In this case, preferably, the through-bores arranged in face-to-face relation in the piston portions are coaxial and the non-return valves are formed as balls being pressed on an opening of the through-bores by a spring being a common one for the coaxial through-bores. Further to this, a throttle can be provided in the through-bore for regulating the speed of flow of the working agent.
In still another preferred embodiment of the working cylinder in this invention, at least one through-channel with a cylinder portion and an end chamber and a bore interconnecting the cylinder portion and the end chamber is provided in each piston portion, and a piston body having a piston sealingly movable in the cylinder portion of the through-channel, a head portion being in the end chamber and a piston rod interconnecting the piston and the head portion and being movable in the bore is arranged in each through-channel. Therein, advantageously, a spring is arranged between the head portion and the piston portion forcing the head portion out of the end chamber of the piston portion.
The objects as set forth hereinabove can be realized according to this invention also by an improvement, wherein a sealing plate is arranged between the two piston portions and the tensed position of the piston portions is established by the interconnection of the sealing plate, and the sealing plate has a middle opening and an outer periphery both being movable on the forced trajectories of the rotational working cylinder in a sealed manner, respectively. Not only the load bearing capacity and the operational range of the rotational working cylinder are enlargened with this improvement but also the manufacture is simpler and cheaper as well as the operational security is greater.
In a preferred embodiment, at least one through-bore being parallel to the shaft is arranged in each piston portion and the opposite through-bores are coaxial and a spring is fixed in every through-bore, an other end of which being fixed to the sealing plate. In this case also, a throttle can be provided in the through-bore for regulating the flow of the working agent into a room provided between the two piston portions.
In another preferred embodiment in this invention, at least one guiding rod fixed at its middle portion to the sealing plate is arranged in coaxially opposite bores of the piston portions, and an inner supporting flange is formed in each bore and a spring is arranged between the sealing plate and the flange as well as between the flange and the guiding rod, respectively, on both sides of the sealing plate. Advantageously, the guiding rod has threaded ends onto which nuts are attached for supporting the springs attached to the guiding rod.
It is also preferable when the sealing plate has a middle plate made of sealing material and two stiffener plates supporting the middle plate from both sides. Therein, it is made possible that the tensioning means providing the tensioned position of the piston portions are connected on both sides to the stiffener plates.